(a) Field of the Invention
The present invention relates to a modulation device and method and a demodulation device and method.
(b) Description of the Related Art
In general, a non-linear modulation scheme such as on-off keying (OOK) in the wireless communication system can use a non-linear power amplifier with great power efficiency. However, the performance of the linear modulation schemes such as the phase shift keying (PSK) or the quadrature amplitude modulation (QAM) with great frequency efficiency is degraded when using the non-linear power amplifiers with power efficiency. Therefore, the PSK or QAM modulation scheme with good frequency efficiency has to use the linear power amplifier, and hence, power consumption of a transmitting device is increased. Therefore, many studies for using non-linear power amplifiers with great power efficiency have progressed in the linear and non-linear modulation schemes so as to reduce the transmitting device's power consumption, which can be generally classified as two approach schemes.
The first scheme is to compensate for distortion of a signal generated by a non-linear characteristic by processing an input signal or an output signal of the non-linear power amplifier. The scheme increases wireless communication system complexity and realization cost since it has to configure a complex compensation circuit at the front or rear part of the non-linear power amplifier.
The second scheme is to reduce the linear power amplifier's power consumption by using a linear power amplifier and controlling a bias voltage of the linear power amplifier. Since the scheme can reduce the realization cost compared to the first scheme, studies for controlling the bias voltage of the linear power amplifier are in progress. As the skill for controlling the linear power amplifier's bias voltage is developed, the relationship between power consumption and an instantaneous envelop form of an input signal of the linear power amplifier becomes more important. According to this viewpoint, the modulation scheme including a silence signal such as the pulse position modulation (PPM) or bi-orthogonal PPM (BPPM) is considered as advantageous in reducing power consumption of the linear power amplifier. However, the PPM or BPPM modulation scheme generates very low frequency efficiency because it has a very long silence signal section.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.